Vehicular communications have been considered to be an enabler for numerous safety and information applications. Many automobile manufacturers are in different stages of integrating communication devices in their vehicles for the purpose of safety, assisted driving, entertainment, and commerce. Numerous projects worldwide, e.g. in Europe, in the U.S. and in Japan, are actively involved in researching and developing the infrastructure for vehicular communications and automotive telematics.
Through vehicular ad-hoc networks, it would be possible to achieve flexible communications among vehicles and with the roadway units or the infrastructure. Multi-hop data dissemination capability is one of the major advantages of vehicular networks. Multi-hop dissemination can be used for enhancing the coverage of safety and emergency warning messages, exchanging neighborhood information queries, etc.
At the same time, the high mobility and the partitioned nature of the networks makes multi-hop data delivery through vehicular networks complicated. Moreover, because of the time-scale of auto manufacturing, it is expected that the fraction of automobiles on the roads equipped with communication radios will be fairly low to begin with and will increase gradually. Due to the low equipped vehicle density, a store and forward method, where vehicles buffer packets and transmit when another vehicle is in range, would be the primary data relaying strategy initially.
Due to the unpredictable nature of vehicular networks, any data dissemination strategy needs to take into account a diverse range of roadway and network parameters such as vehicle speeds, direction, density radio range, roadway lengths etc. Also, numerous safety applications require group-based communication. To cater to such requirements, various broadcast and flooding protocols have been considered, such as message dissemination using local attributes, e.g., position and direction, broadcast interval, and roadway segments, as well as a mobility centric approach for data dissemination (MDDV), which provides a hybrid approach for reaching geocast areas and providing local dissemination based on source defined trajectories, and dynamic organization of vehicles into peer groups for efficient local information dissemination.
Further, for end-to-end communication, various position based routing protocols have also been proposed for vehicle ad hoc networks. Position-based routing consists of 1) a location service which maps node ID (IP address) to geographical position (GPS); and 2) a forwarding scheme which selects the next hop based on the geographical information of the node, neighbors, destination, and other mobility parameters.
As a result of the high variability of the parameters, it is difficult for heuristic based forwarding methods to function well under the entire range of network conditions. While characterization and modeling of various parameters of vehicular networks such as mobility, wireless channel, delay performance have already received significant attention, there is a need for optimal algorithms based on available system characterization methods.